Recently, there has been a trend toward controlling the operation of safety equipment according to the weight and constitution of a person's body in order to improve the performance of seat belts and air bags. For example, the vehicle judges whether the person getting therein is a child or an adult, and adjusts an expanding gas quantity and an expanding speed or stops the operation of the air bag. Therefore, it is necessary to know the weight of the person sitting on the seat by using some means. As an example of such means, a system is proposed in that a strain sensor (load cell) is disposed at four corners of seat rails in order to measure the weight of the person by adding the loads vertically applied to the load cell (Japanese Patent Laid-open Publication H11-1153).
As for a strain sensor for the person weight measuring equipment, there is a demand for a small-sized sensor whose maximum measuring load is about 50 kg. As such strain sensors, there are those having a strain gauge stuck (or formed) on a sensor plate which is deformed by the load, those based on a piezoelectric system, and those using a static capacity sensor for detecting the displacement of an elastic member which is deformed by the load.
In a case of such a weight measuring device and person weight measuring equipment using same, the load of the object to be measured is directly applied to the strain detectors disposed in the equipment. Therefore, there arises a problem of a reduction in detecting resolution if priority is given to an assurance of strength of the detectors.
The present invention is intended to address such problem, and the object of the invention is to provide a weight measuring device and a person weight measuring equipment using the same. The weight measuring device can improve the detecting resolution by reducing the load applied to the strain detector as much as possible.